San Francisco to Los Angeles the slow way, with Big Sur in the middle.
The stretch of Highway 1 between San Francisco and Los Angeles is the most over-photographed road in America and still worth doing. The reason is Big Sur: ninety miles of cliff road with almost no development, where the driving itself is the attraction rather than the transit between attractions.
Drive it north to south so the ocean is on your side of the road and the pull-outs are right-hand turns. Check Caltrans before you commit — Highway 1 through Big Sur closes for landslides more often than people expect, sometimes for months.
Four people in one car turns an expensive trip into a reasonable one, but Big Sur accommodation doesn't scale — you'll likely need two rooms. Sort the driving rotation and the fuel-splitting rule on day one, and keep the night-by-night bookings somewhere everyone can see, because there's no signal to sort it out on the road.